Think of all the different animals that you can. Make a list of all the ones that you know about--cats, dogs, elephants, giraffes, lions, tigers, bears, bugs. Now add to the list all of the plants that you can think of--pine trees, palm trees, carrots, apples trees, lettuce, cactus, grass. Combining these will create a long list of things is hard to look at and even harder to study from. There are more than 1.5 million species of organisms that have been identified by scientists. In order to study all of these organisms, scientists have put them into different categories, in other words, they classify them.